#include <bits/stdc++.h>

using namespace std;

struct ListNode
{
    int val;
    ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};

class Solution
{
public:
    bool hasCycle(ListNode *head)
    {
        ListNode *fast, *slow;
        slow = head;
        fast = head;
        while (fast && fast->next)
        {
            slow = slow->next;
            fast = fast->next->next;
            if (fast == slow)
            {
                return true;
            }
        }
        return false;
    }
};